Carter is almost 12 weeks old and around 12lbs. He can still fit in his KL0 although the absorbancy on the 1's are better since they're bigger. What I've been doing with the 0 is snapping the wing to the leg snap, it seems to make a tighter fit and he can wear it longer.

Edit: Oh I see your daughter is 1 day older than my son I would with the 1's.